Spacing problem with \phantom in array

Question

Using

$\begin{array}{ccc}
x & := & \phantom{ a + } b + c\\
y & := & a \phantom{ + b } + c\\
z & := & a + b \phantom{ + c }
\end{array}$

I get

which is not quite what I hoped for as my "phantoms" don't take as much space as expected.

How can I correct this?

Thanks!

Answer 1

In the final part of the first row, try \phantom{a+{}}b+c to make the first plus sign act like a "real" math-binary element. Similarly, you'll also need to adjust the second row to a\phantom{{}+b}+c.